In rotary die-cut apparatus, which may form a section of a flexographic printer die-cutter machine, a die roll carrying one or more die blades cuts paperboard sheets against a supporting anvil roll. The paperboard sheets are fed successively through a nip formed between the cooperating die and anvil rolls. Both the rolls are rotatably driven, usually the anvil roll being driven via gearing from the die roll. The anvil roll has a resilient cover into which the blade or blades of the die roll penetrate during the die-cutting of the sheets. Such die-cutting may comprise scoring the sheets, to form fold lines, and/or making complete cuts through the sheets. Usually the die blades are serrated. The penetration of these blades repeatedly into the resilient cover tend, in time, to cut and tear the surface of the cover. It then becomes necessary to replace this cover. During this wearing of the cover, the cover surface becomes irregular and the overall diameter of the covered roll reduces.
The anvil roll may be mounted in the frame of the machine such that it can be adjustably moved towards the die roll from time to time as the cover wears. Also, arrangements have been suggested and tried for rotating the anvil roll at a slightly different speed of rotation to the die roll. One such arrangement used is the "one tooth hunting ratio" whereby the die and anvil rolls are rotationally interconnected by a pair of gears, one of these gears having one gear tooth less than the other. For example, the die roll gear may have 131 teeth and the anvil roll gear 130. In this way the cutting pattern of the die blades into the anvil roll cover only starts repeating again after 130 revolutions of the anvil roll. This slows down the wear rate of the anvil cover. But as these rolls usually rotate at more than 100 rpm, for example 170 rpm, this repeating cutting pattern of the anvil roll cover occurs fairly frequently.